Many systems have been proposed and used to remove bacterial growth and the like from surfaces in a water system. Some systems, such as disclosed in U.S. Pat. No. 4,892,148 issued Jan. 9, 1990 to James A. Mason and U.S. Pat. No. 5,719,100 issued Feb. 17, 1998 to Zradnick, et al use sodium chlorite and citric acid to treat water. These two patents are hereby incorporated in their entirety by reference. Systems such as these result in cleaning but the production of chlorine dioxide is relatively slow and the oxidizing effect of the solution is quickly spent when the solution is prepared offsite or even if the materials are injected for reaction in-situ. Such processes also result in the production of hydrochloric acid and sulfuric acid when materials such as iron sulfide are present in the formation.
In industrial water systems, such as open recirculating cooling systems, once through systems or closed systems, iron can form deposits. The iron can enter the system via make up water, which is used to replace that lost through evaporation. While this is one source of iron, the majority of the iron comes from corrosion of ferrous metals in the system. Iron deposits are very thermally insulating and losses in heat transfer occur, thus it is desirable to remove these deposits. Two methods of removing these deposits have been used. i.e., “on-line” and “off-line”. When such fouling occurs it is not uncommon to mechanically or chemically clean the iron off the metal surfaces. Some types of cleaning require that the unit being treated be shut down (off-line). Such shut-downs can result in production losses, which are generally very expensive. In addition, off-line cleaning typically generates a substantial amount of waste solution, which can be hazardous depending upon what, and how much is present. An example of off-line cleaning is given in U.S. Pat. No. 4,190,463 issued Feb. 26, 1986 to Roy L, Kaplan, which is hereby incorporated in its entirety by reference.
Obviously in situations such as heat exchangers in which water is used as a heat exchange fluid, the presence of such deposits is very undesirable and can greatly reduce the effectiveness of the heat exchange equipment. One process for removing these materials is the use of acids. While this has been limitedly effective and will reduce deposits such as lime deposits which may also exist in such systems, the strong acids required are very corrosive to the ferrous equipment in which they are used. Accordingly, such clean ups may damage the equipment in the process of removing a portion of the iron salts and deposits as well as any other deposits in the area.
Another area of interest is the production of fluids from subterranean formations. Water wells are prone to deposits of iron compounds on surfaces where the water emerges from the subterranean water-bearing formation or on the surfaces of the fluid-producing equipment. This iron may come from ferrous components in the water-producing equipment in the system or from the formation itself. Similarly biological growth may occur in such systems. While the use of chlorine produced at the surface and injected may be effective to remove the biological growth it is not generally effective for removal of iron deposits. Again these deposits can be very detrimental in that they may restrict the flow of fluids and may affect the performance of the equipment required to produce the fluids.
Particularly in oil or gas wells where the wells may produce at least one of oil or gas in addition to water, it is well known that bacterial growth can occur in many areas in the well. These deposits can have the effect of forming hydrogen sulfide, which is a corrosive by-product.
Chlorine is a strong oxidizer and has been used for many years for treating water. Its action is well known and very effective at low levels. There are also a number of other oxy-chlorine compounds available, which are powerful oxidizers and can be used in place of chlorine. These materials have the advantages of biocidal activity, the ability to react with ferrous and other sulfides to produce sulfates and the ability to oxidize ferrous deposits in place. Through proper product design and application, certain of these materials can be effectively applied to problems in the oil fields. These materials, however, typically have the disadvantage that while oxidizing biocidal materials and oxidizing sulfide salts of iron, the iron is converted from ferrous iron to ferric iron which has a much lower solubility in water. Reacted materials may produce strong mineral acids, if present in sufficient quantities, and can dissolve some of the ferric iron deposits. However, these acids can be damaging to ferrous materials in the system for producing fluids from the particular formation.
Accordingly it is highly desirable that a system be available which can be used in all these systems to remove iron deposits, biocidal deposits and the like by solublizing the iron without adversely affecting the ferrous materials used to fabricate the fluid recovery or fluid handling system.
Accordingly a search has continued for a formulation which can be used to achieve these objectives without damaging ferrous equipment in water systems.